Colonisation of the Americas at the end of the 15th Century killed so many people, it disturbed Earth’s climate.

That’s the conclusion of scientists from University College London, UK.

The team says the disruption that followed European settlement led to a huge swathe of abandoned agricultural land being reclaimed by fast-growing trees and other vegetation.

This pulled down enough carbon dioxide (CO₂) from the atmosphere to eventually chill the planet.

And their basis for this is…

The team reviewed all the population data it could find on how many people were living in the Americas prior to first contact with Europeans in 1492.

It then assessed how the numbers changed in following decades as the continents were ravaged by introduced disease (smallpox, measles, etc), warfare, slavery and societal collapse.

It’s the UCL group’s estimate that 60 million people were living across the Americas at the end of the 15th Century (about 10% of the world’s total population), and that this was reduced to just five or six million within a hundred years.